I came across this yesterday as I was looking for nyckelharpa info, and went ahead and downloaded it in hopes I could get a decent audio rip for my mp3 collection. I found myself utterly fascinated. Why? I think I've mentioned before that music always creates impressions of images in my mind that can best be described as spots and ribbons of various hues and brightnesses. This video comes closer than anything I have ever seen at roughly approximating the kinds of things I see in my mind when I hear music. One reason I so love Bach and organ music in general is because of the intense layering of varying colors and textures they generate.
More at Music Animation Machine.